A semiconductor product is produced through the step of forming a photosensitive resin as an etching resist on a semiconductor wafer and subjecting the semiconductor wafer to etching, and the like steps.
This photosensitive resin is liquid, and is applied onto a surface of the semiconductor wafer, using a spin coater or the like. In order to scatter solvent and so on after the application, the resin must be dried. Thus, the semiconductor wafer subjected to the application is put on a heater and heated.
Hitherto, as a heater made of metal and used for such a purpose, a heater wherein heating elements are arranged on the back surface of an aluminum plate is adopted.
However, such a heater made of metal has the following problems.
First, the thickness of the heater must be as thick as about 15 mm since the heater is made of metal. This is because a warp, a strain and so on are generated in a thin metal plate because of thermal expansion resulting from heating so that a semiconductor wafer put on the metal plate is damaged or inclined. However, if the thickness of the heater is made thick, problems such that the heater becomes heavy and bulky arise.
Heating temperature is controlled by changing the voltage or amperage applied to the heating elements. However, if the metal plate is thick, the temperature of the heater plate does not follow the change in the voltage or amperage promptly. Thus, a problem that the temperature cannot be easily controlled is caused.
Thus, as described in Japanese Kokai Publication Hei 9-306642, Japanese Kokai Publication Hei 4-324276, Japanese Kokai Publication Hei 7-280462, U.S. Pat. No. 5,643,483 Specification and so on, ceramic heaters wherein AlN, which is a non-oxidized ceramic having a large thermal conductivity and a large strength, is used as a substrate and heating elements are formed on a surface of this AlN substrate or inside the AlN substrate are suggested.
Such a ceramic heater is usually used, being fitted into a supporting case through a seal ring.